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In the present paper the effect of repeated lengthening exercise on the expression of cytoskeletal proteins was studied in rat skeletal muscle. Tibialis anterior muscles were subjected to an exercise session consisting of 240 lengthening (L) or shortening (S) contractions. Muscles were excised 4 days post-exercise. Contralateral muscles served as controls (C). Western blotting was done with antibodies against desmin and vimentin. In C and S immunostaining yielded a regular cross-striated pattern, in L however, fibers can be detected without immunostaining. Western blots showed no major differences in the amount of desmin between C, S and L, although some proteolysis was present in L. Vimentin was absent in C and S, and prominently present in L. These data indicate that remodeling of the intermediate filament lattice after damage induced by lengthening exercise occurs in a differentiation like manner.

An in vivo method for measuring local deformations of the surface of skeletal muscles is presented. The method was applied to the aponeurosis of the medial gastrocnemius muscle (MG) of cat. Approximately 150 fluorescent polystyrene markers were attached to the aponeurosis and the distal muscle fibres of the MG. Two-dimensional video recordings of the muscle-tendon complex in situ during active force production at fixed muscle length were made. Principal strains (ε1 and ε2) and strains in the longitudinal direction of the muscle-tendon complex (εlon) and in the transverse direction (εt) were calculated. The aponeurosis extended during contraction of the MG. Mean longitudinal strain of the aponeurosis was approximately 2%. An increase in strain was found in the disto-proximal direction. In the transverse direction, large inhomogeneities in the strain were found.

We present a hydrodynamic model of suction feeding of a 6.5 mm carp larva, calculated from the streamlines and fluid particle pathlines observed. From this model we also have calculated the accelerations of the water near the mouth aperture (which reach 800 m/s2) and the path lines of actively accelerating fluid particles (which mimic 'escaping prey'). The shape of the parcel of water sucked into the mouth cavity is almost spherical, due to the prevalence of suction flow over swimming velocity. This parcel of water is entirely in front of the initial position of the larva. We suggest that the low velocity of swimming and the absence of protrusion of the mouth are functionally coupled with the high inaccuracy of aiming of young fish larvae. For a prey starting in the centre of this parcel of water the best direction for escape is forward. The velocity required for escaping radially is twice as high as for escaping forwards. Optimum sucking techniques for fish larvae are discussed.